WO2010062200A1

WO2010062200A1 - Improvements to energizers

Info

Publication number: WO2010062200A1
Application number: PCT/NZ2009/000262
Authority: WO
Inventors: Richard Lloyd Johnston; George William Tyler; Murray Donald Long
Original assignee: Gallagher Group Limited
Priority date: 2008-11-26
Filing date: 2009-11-26
Publication date: 2010-06-03
Also published as: NZ573113A

Abstract

A method of operating an electric fence energizer, including the steps of transmitting a low voltage signal from an output of the energizer onto an electric fence, determining the load on the electric fence by monitoring the low voltage signal, determining an appropriate energy level for a high voltage pulse relative to the load, and generating and transmitting the high voltage pulse from the output of the energizer onto the electric fence according to the energy level determined to be appropriate.

Description

IMPROVEMENTS TO ENERGIZERS

TECHNICAL FIELD

This invention relates to improvements and modifications to electric fence energizers.

BACKGROUND ART

Electric fence energizers are well known for use in the control of animals and have been in use for over 50 years. The most common circuit topology for generating an electric impulse for powering an electric fence has not changed significantly over this time. In this topology a capacitor is charged up to a preselected voltage by a mains or battery power supply. The capacitor is then discharged through an output transformer primary at some preselected interval of not less than 1 second, in order to comply with safety standards. The energy from the capacitor is transferred through the magnetic flux in the core of the output transformer to the secondary of the output transformer and onto the fence in the form of a pulse.

There are circumstances where an electric fence is heavily loaded by contact with vegetation. Under these circumstances the electric fence energizer powering that fence can be required to output many joules of energy in order to maintain an acceptable voltage on the fence.

There can be circumstances where a human makes contact with the electric fence and can receive a shock containing energy intended for the heavily loaded fence. Circuit topologies have been developed which intend to limit the energy and resulting shock to the human contacting the fence, by sensing the load on the fence at or prior to the time the pulse has been released from the energizer onto the fence and limiting the energy accordingly. These systems have been ineffective, as the load on the fence has been traditionally sensed during the previous pulse. Accordingly if a human comes into contact with the fence after a pulse has passed, the next pulse from which they receive a shock will not have adjusted for the heavier load due to human contact. They will therefore receive a potentially larger shock than is desired.

Numerous efforts have been made to overcome these problems.

New Zealand Patent No. 240641 discloses a technique which senses the load on the output of an energizer supplying a pulse to a fence system and the stored energy is adjusted in response to the perceived load, subsequently reducing or increasing the amount of energy stored in order to power the fence as required.

In New Zealand Patent No. 509061 and European Patent No. 1297729, multiple banks of capacitors are progressively switched in or out depending on the load sensed on the output of the energizer, allowing the energy output of the next output pulse to be adjusted according to the sensed load or rate of change of the sensed load.

The above solutions have problems in that they use a high voltage pulse to sense the load on the fence, before reducing the energy output of the next pulse if necessary. In doing so, a human touching the fence still receives at least one high energy shock. Additionally, these systems use a sense pulse for sensing the load during the time normally available for the deterrent pulse. Because the deterrent pulses may only be sent at specified intervals, the effectiveness of the fence is reduced.

The use of any high voltage to sense a change in load may be undesirable in certain circumstances. All previous approaches discussed require the use of at least a portion of a high voltage pulse to determine if it is appropriate to output more of the high voltage pulse (or further high voltage pulses). Safety Standard IEC/TS 60479-1 Effects of Electric Shock on the Human Body states that "For a given current path through the human body, the danger to persons depends mainly on the magnitude and duration of the current flow". Therefore any energizer using a high voltage sense pulse is significantly increasing the risk to humans by increasing the pulse duration to that of at least the sense pulse duration plus the main pulse duration.

It would be advantageous to detect the load (and therefore risk of human contact) before decisions are made about outputting a high voltage pulse.

More recently, energizer designs have promoted the use of controllable switching devices such as IGBT or MOSFETS that can be turned on or off to control the output energy supplied to the load depending on the requirement, as in UK Patent No. GB 2403856A and New Zealand Patent No. 535719.

The problem with these systems is the high cost of the switching devices. Further, an inherent safety issue exists with having a large amount of energy stored in a capacitor, where stopping the discharge of the capacitor in mid flight to limit the energy transmitted to the load can result in catastrophic failure.

PCT Publication No. WO 2008/095160 discloses a detection system that injects a low voltage signal at the fence terminal end of a security electric fence, and senses a short or open circuit at the return end of the wire.

The device disclosed in WO2008/095160 is not suitable for agricultural electric fencing applications where the wire end away from the energizer output terminal is usually not accessible. Further, the purpose of low voltage sensing in security electric fencing is to signal an alarm when a short or open circuit is detected rather than for the purposes of adjusting the output of the high power pulse to an appropriate level. Improved control and efficiency of energizers in response to a detected load is therefore desired.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a method of operating an electric fence energizer, including the steps of:

- transmitting a low voltage signal from an output of the energizer onto an electric fence;

determining the load on the electric fence by monitoring the low voltage signal; - determining an appropriate energy level for a high voltage pulse relative to the load; and

- generating and transmitting the high voltage pulse from the output terminal of the energizer onto the electric fence according to the energy level determined to be appropriate.

According to another aspect of the present invention there is provided a method of operating an electric fence energiser as described above, including the steps of:

- transmitting a second low voltage signal from the output;

- determining the new load on the electric fence by monitoring the low voltage signal; and

- determining an appropriate energy level for the high voltage pulse relative to a change in load.

According to a further aspect of the present invention there is provided a computer program configured to be operable by a processor to carry out a method for operating an electric fence energizer, as described above.

According to a further aspect of the present invention there is provided an electric fence energizer including:

a low voltage signal generator configured to transmit a low voltage signal from an output of the energizer;

a low voltage signal device configured to obtain an electrical parameter of the low voltage signal;

a controller configured to determine the load on the output of the energizer from the electrical parameter; a high voltage pulse generator configured to generate and transmit a high voltage pulse from the output of the energizer,

characterised in that

the controller is configured to determine an appropriate energy level for the high voltage pulse relative to the load, and control the generation and transmission of the high voltage pulse according to the energy level determined to be appropriate.

It is envisaged that the energy level of the high voltage pulse determined to be appropriate may be defined by electric fence safety standards such as IEC 60335- 2-76, EN60335-2-76, or UL69 under the output characteristics clauses of the applicable standard.

For example, IEC 60335-2-76 allows a maximum RMS current dependent on the pulse duration, which is prescribed by the C2 curve graph of the standard. EN60335-2-76 allows for a maximum of 5 joules to be transmitted, measured into a range of test loads. It should be appreciated that the precise characteristics required by a standard may change from time to time.

One skilled in the art would recognise that this is not intended to be limiting, and the energy level of the high voltage pulse may be defined by any set of standards - whether regulated or independent of international standard setting authorities.

The low voltage signal may be formed in any way known to one skilled in the art, including (without limitation) a sine or square wave, a low voltage single pulse or a burst of pulses or a direct current (DC) voltage.

In preferred embodiments the low voltage signal may be "Safety Extra Low Voltage" (SELV) or "Extra Low Voltage" (ELV) depending on the power source of the energizer. Reference to ELV should be understood to mean the electrical potential of any conductor against earth as being not more than either 42.4 volts peak for alternating current, or 42.4 volts peak for direct current, in accordance with the definition set out by the International Electrotechnical Commission (IEC) in publication 60335-1-76.

SELV should be understood to be a voltage which cannot exceed ELV under normal conditions, and that is isolated from the supply mains by a suitable isolating transformer.

One skilled in the art would recognise that reference to these terms is not intended to limit the voltage levels of the low voltage signal in all applications, and is intended to provide context to the application of the present invention. However, the low voltage signal will preferably be less than 42.4 volts, and contain less than 5% of the energy of the allowable high voltage deterrent pulse

In comparison with the maximum allowable levels of a deterrent pulse the voltage magnitude and energy level of the low voltage signal are negligible. As a result, determination of a safe energy level for the high voltage pulse may effectively ignore the low voltage signal.

Having the low voltage signal as ELV or SELV allows the load or change in load on the electric fence to be measured dynamically at any time other than during the high voltage deterrent pulse. This is generally 99.99% of any 1 second period that contains a 100 microsecond pulse, and the signal may effectively be on the fence continuously.

Alternatively, the low voltage signal may not be on the fence continuously, but may be sent over a predetermined period just prior to launching the deterrent pulse. This may reduce the energy used by the energizer in maintaining the low voltage sensing signal.

Generation of the high voltage pulse may be achieved in any way known to those skilled in the art. The power source for the high voltage pulse generator may be via mains power, battery, solar panel or any other source of electrical power.

Preferably, the desired quantity of energy for the high voltage pulse will be stored in an energy storage element before transmission. In a preferred embodiment the energy storage element may be provided by at least one capacitor. It should be understood by one skilled in the art that this is not intended to be limiting, and that other energy storage components and configurations are envisioned and within the scope of the present invention.

The high voltage pulse generated will preferably be 7000 to 10000 volts and contain a level of energy suitable for the sensed load or change in load.

In some embodiments the energizer may utilise an output transformer, such as those known in the art. An output transformer provides a step up in voltage from the power source or energy storage device. This may be required to achieve a level of voltage of the high voltage pulses desirable for deterrent purposes.

Reference to the secondary side of a high voltage output pulse transformer should be understood to mean any direct connection to a fence circuit. Reference to the primary side of a high voltage output pulse transformer means connection to that part of the energizer electrically isolated from a fence circuit by the transformer.

An output transformer may also contain the requisite isolation from mains voltage specified by the previously mentioned electric fence safety standards. In the case of a battery powered energizer, it may be that no such isolation is required. It is envisaged that the low voltage signal may be generated on either the primary or secondary side of the output transformer.

It is envisaged that the low voltage signal may be generated by a dedicated low voltage generator circuit. In doing so, the low voltage generator would be electrically isolated from the high voltage generating circuitry.

However, this should not be seen to be limiting, and the low voltage signal may be generated in other ways.

For example, the low voltage generator may include a processor configured to control the high voltage pulse generator to adjust the stored voltage level on the main storage capacitor used for generation of the high voltage pulse. In doing so, existing components are used for both the high voltage pulse and low voltage signal generation. This may reduce initial costs associated with manufacture and design due to the additional components and circuit complexity. Costs associated with replacement and repair of these parts may also be reduced.

It is known in some electric fence systems to provide a low voltage communications circuit for the transmission of communication signals on the fence line. Where the communications signal is below 42.4 volts, this communications circuit may be used for the purpose of generating the low voltage signal and sensing the load or change in load of the fence line.

Again, redundancy in terms of additional components is avoided, which may improve the cost efficiency of the system.

It is envisaged that implementation of the present invention may be achieved by the installing of a software upgrade consisting of a computer program or computer executable instructions configured to be executed by a processor in an existing energizer design to carry out a method of operating the energizer, as described herein. This may significantly reduce costs to users who have already installed energizer systems that do not comply with the previously described safety standards.

Further, monitoring of the low voltage signal may be carried out on either the primary or secondary side of the output transformer.

It is envisaged that the low voltage sensing device configured to monitor the low voltage signal will typically sense an electrical parameter such as voltage, current, phase angle or any other parameter associated with any measurable change in the low voltage signal due to any change in load on the output of the energizer.

It is envisaged that the energizer may include a high voltage sensing device for the sensing and measurement of electrical parameter(s) associated with the high voltage pulse. Measurement of the electrical parameter may be used to determine the change in load on the fence in order to confirm or verify the measurement of an electrical parameter associated with the low voltage signal.

If the measurement of the low voltage signal is not verified, then the energy level of the high voltage pulse may be limited to below a predetermined level, for example 5 Joules, and an alarm issued indicating a fault.

An advantage of using this technique of verification is that it may remove the need for additional and potentially redundant components for checking that the low voltage generation and sensing systems are operating correctly.

It is envisaged that determination of the value of the load from the sensed electrical parameter of the low voltage signal will be made by a controller. This should not be seen as limiting, as in some embodiments this determination may be made by the low voltage sensing device. The value of the load may then be transmitted to the controller. The controller may also carry out determination of the safe or appropriate energy level of the subsequent high voltage pulse. The controller may be a processor running computer code which will implement decision making algorithms. A processor may be any conventional processor, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other combination.

However one skilled in the art would appreciate that this is not intended to be limiting, and the controller may be analogue or digital hardware that utilises predetermined thresholds to determine the appropriate energy level for the high voltage pulse.

For example, if the load on the output terminal of the energizer is determined to be 500 ohms, then the maximum energy level of a high voltage pulse to be transmitted onto the output may be predetermined to be 5 joules. If the load remains substantially constant on the output for more than a predetermined period of time (for example 5 minutes), then the controller may determine that the steady state load is due to vegetation loading the fence and allow the transmission of a high voltage pulse having a greater energy level (for example 10 joules). On detection of any change in the load, the controller may restrict the energy level of any further high voltage pulse to the previously predetermined maximum energy level of 5 joules.

It is envisaged that the controller may also control the high voltage pulse generation of the energizer. However this is not intended to be limiting, and it should be appreciated that a separate device in communication with the controller may be responsible for monitoring the generation of the high voltage pulses. In situations where the detected load or change in load is indicative of a human being in contact with the fence, the energy level may be limited to below 5 Joules.

It is envisaged that changes in load beyond certain limits will result in output of the high voltage pulse being inhibited or an alarm issued.

Altering the energy level of the high voltage pulse may be achieved in a number of ways. The controller may inhibit the pulse from being emitted from the output until the energy stored on the main storage capacitor has been reduced or charged to a desired level.

Alternatively, the controller may control the number of capacitors discharged from a bank of capacitors according to the desired energy level. The controller may also divert a portion of the energy stored to a secondary storage device so that it is not discharged from the output. It should be appreciated that this is not intended to be limiting and that any other method for altering the energy level of an electrical pulse known to those skilled in the art may be utilised.

It should be appreciated that reference to specific energy storage components, such as capacitors, is not intended to be limiting, and the present invention may utilise any method or hardware for the generation or control of high voltage pulses known to those skilled in the art.

It is envisaged that monitoring of the load and subsequent adjustment of the high voltage pulse may account for a variety of situations.

Load off detection in the context of the present invention refers to the situation where the impedance of the load at the output terminals of the energizer is detected as increasing, for example from 100 ohms to 500 or 1000 ohms. Load on detection in the context of the present invention refers to the situation where the impedance of the load at the output terminals of the energizer is detected as decreasing, for example from 500 ohms to 100 ohms.

It is envisaged that where the low voltage sensing signal is used for load off only detection, the energizer may be configured such that its output impedance has a maximum energy transfer characteristic at a particular impedance point.

When this impedance point is reached in the case of a heavier load being_. applied to the fence, efficiency of the energizer will decrease. This results in a predetermined maximum amount of energy being output in the form of the high voltage pulse. This may protect the transient load, such as a human connected in series with the steady state load, from being exposed to a high voltage pulse having a dangerous level of energy.

When the load has stabilised for some period of time, for example 1 minute, that load becomes the steady state load. This indicates the load is purely farm fence load. The energizer may then increase the amount of energy output in the high voltage pulse, while still remaining below a predetermined maximum level.

Reference to the load having stabilized should be understood to mean that the load has not changed beyond predetermined limits over a predetermined period of time.

However, when a load comes off the fence there is a risk that a higher than acceptable amount of energy may go into the new and lighter load, which may be a human. In this instance the low voltage sensing device may transmit this information to the controller which will limit the amount of energy that may be output into the new lighter load under transient conditions.

Also if the low voltage sensing device detects that the load on the output of the energizer has become lighter, for example changing from 100 ohms to 1000 ohms then this may be indicative of a large portion of farm fence being disconnected from the output of the energizer. Limiting the energy of high energy pulses output onto the fence under these conditions is desirable as this eliminates the risk that a human load will receive the level of energy intended for a highly loaded fence.

There is an added advantage in the reduction of stress on electronic components within the energizer. If the energy was not limited, these components would be required to discharge or dissipate a high level of energy not delivered to the lighter than expected external load. This stress may cause a deviation in the operating characteristics of the components, or even catastrophic failure.

It is anticipated that an increasing load on the output of the energizer may cause a decrease in the magnitude of the low voltage sensing signal. This decrease in magnitude may be detected by the low voltage sensing device and this information transmitted to the controller. The controller may subsequently limit the amount of energy that is transmitted in the high voltage pulse.

The low voltage sensing device and controller may continue to monitor the load on the fence. If the load is determined to have stabilised after some period of time, for example 15 seconds, there is a low probability that a human is in contact with the fence. The controller may then allow higher energy pulses to be transmitted onto the fence.

The present invention provides the following advantages:

• Providing a more effective and safety standard compliant high voltage pulse whilst retaining the ability to sense load changes on the fence. As the energy of the low voltage sensing signal is negligible compared to the high voltage pulse, the sensing signal may be effectively discounted when considering the limitations to the high voltage pulse required by any particular safety standard; . • Reducing risk to humans or animals receiving deterrent pulse energies and increased deterrent pulse duration beyond limits set by standards, by using a low voltage sensing signal followed by the high voltage pulse - as opposed to a high voltage sensing signal followed by the high voltage pulse;

• Low voltage sensing ensures no high voltage pulses are output onto the fence, whether for detection or deterrent purposes. This presents a much lower risk than other high voltage load sensing methods which require the output of a high voltage sensing signal in order to determine whether output of a further deterrent pulse is safe.

• Immediate detection of any changes in the load through the use of a low voltage signal allowing continuous sensing of the output load;

• Alternatively, increasing power efficiency of the energizer is achieved by transmitting the low voltage signal in a short burst which senses the load just prior to transmitting the high voltage pulse. This may reduce ongoing costs due to power usage. This is particularly relevant to limited power sources such as battery or solar power energizers;

• Inherent capability to safely operate under both the less common load off condition in addition to the more common load on condition. Other sensing methods are directed to the load on condition and may fail to account for all circumstances which pose a risk to humans; and

• Reduced costs in circuit design and manufacture by the use of existing components or complete energizer systems. Further, the potential for a software only upgrade reduces costs and is more convenient for users having energizer systems that do not comply with safety standards. BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of a first circuit to be used in some embodiments of the present invention.

Figure 2 shows a schematic diagram of a second circuit to be used in some embodiments of the present invention.

Figure 3 shows a schematic diagram of a third circuit to be used in some embodiments of the present invention.

Figure 4 shows a schematic diagram of a fourth circuit to be used in some embodiments of the present invention.

Figure 5 shows a schematic diagram of a fifth circuit to be used in some embodiments of the present invention.

Figure 6a, 6b show graphical representations of voltage and impedance waveforms across the output of the energizer in accordance with one mode of operation of the present invention.

Figure 7a, 7b show graphical representations of voltage and impedance waveforms across the output of the energizer in accordance with a further mode of operation of the present invention.

Figure 8a, 8b show graphical representations of voltage and impedance waveforms across the output of the energizer in accordance with a further mode of operation of the present invention. Figure 9a. 9b show graphical representations of voltage and impedance waveforms across the output of the energizer in accordance with a further mode of operation of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 is a schematic diagram of an electric fence energizer in accordance with one embodiment of the present invention.

The energizer (generally indicated by arrow 1) includes a high voltage pulse generator (2).

The high voltage pulse generator (2) is connected to the primary side of an output transformer (3). The secondary side of the output transformer (3) is connected to the output terminals (4, 5) of the energizer.

The output terminals (4, 5) are connected to an electric fence load (6).

The energizer (1) includes a low voltage signal generator (7).

The low voltage signal generator (7) is connected to the primary side of the output transformer (3). The low voltage signal generator (7) is configured to generate a low voltage signal and transmit the signal to the output (4, 5) of the energizer (1).

The energizer (1) also includes a low voltage sensing device (8). The low voltage sensing device (8) is connected to the primary side of the output transformer (3), and is configured to detect an electrical parameter of the low voltage signal which is dependant on the impedance of the load (6). This electrical parameter is the amplitude of the voltage of the signal.

The low voltage sensing device (8) is connected to a controller (9). The controller (9) is configured to receive transmissions from the low voltage sensing device (8) with regard to the electrical parameter detected.

The controller (9) is configured to determine the value of the load (6) or change in the load (6) and subsequently determine the safe or appropriate level of energy or current for the next high voltage pulse to be generated. Alternatively, the controller (9) may determine that a high voltage pulse should not be generated in response to the present state of the load.

The controller (9) is also configured to initiate the generation and transmission of the high voltage pulse from the high voltage pulse generator (2) to the output (4, 5) of the energizer (1) in accordance with the desired energy levels and timing of the pulse.

Figure 2 is a schematic diagram of an electric fence energizer (1) in accordance with a further embodiment of the present invention.

The energizer (1) is substantially the same as that of Figure 1 , with the low voltage sensing device (8) configured to connect to the secondary side of the output transformer (3).

Similarly, Figure 3 depicts the energizer (1) with the low voltage sensing device (8) configured to connect to the primary side of the output transformer (3), and the low voltage signal generator (7) connected to the secondary side of the output transformer (3).

Figure 4 shows the energizer (1) with both the low voltage sensing device (8) and low voltage signal generator (7) connected to the secondary side of the output transformer (3).

Figure 5 shows an energizer (1) as described with reference to Figure 1 , including a high voltage sensing device (10). The high voltage sensing device (10) is connected to the secondary side of the output transformer (3) and is configured to detect an electrical parameter of the high voltage pulse which is dependant on the impedance of the load (6).

The high voltage sensing device (10) is connected to the controller (9), and is configured to transmit information regarding the electrical parameter of the high voltage pulse to the controller (9).

The controller (9) may then use this information to determine the value of the load (6) and verify the measurements made by the low voltage sensing device (8). In the event that the calculated value of the load (6) obtained by the low voltage sensing device (8) is not verified, the controller (9) limits the energy level of the high energy pulse generated by the high voltage pulse generator (2) to an appropriate level.

The energizer (1) includes an alarm device (11), and the controller (9) is configured to issue an alarm indicating that a fault has occurred in determining the value of the load (6). It should be appreciated that this alarm device (11) may be implemented in any of the configurations of the energizer (1) described with reference to Figures 1 - 4. The alarm device (11) is configured to issue an alarm when a particular load condition is detected, not just when the measurement of the low voltage sensing device (8) is not verified.

Figure 6a shows a graphical representation of the low voltage signal generated by the low voltage generator (7), at the output (4, 5) of the energizer (1) of Figures 1 - 5. Figure 6b shows a graphical indication of the impedance of the load (6) on the same time scale.

At point (20) the low voltage sensing device (8) senses the amplitude of the low voltage signal of Figure 6a and transmits this measurement to the controller (9) which interprets the low voltage measurement and converts it to an indication of the load (6), as depicted by Figure 6b at point (20). If this load has been stable for a predetermined time, and is also less than a predetermined value, then the controller (9) controls the amount of energy or current to be provided by the high voltage pulse generator (2) to the output (4, 5) of the energizer (1) in the pulse as shown at point (21) of Figure 6a.

This process is repeated at points (22) and (23) of Figure 6a.

At point (24) of Figure 6b, the impedance of the load (6) is shown to increase, before the next high voltage pulse. At point (25) a low voltage signal burst is transmitted to the output (4, 5) of the energizer (1), the low voltage sensing device (8) measures the amplitude of the low voltage signal, and conveys this measurement to the controller (9). The controller (9) reduces the energy available for the high voltage pulse generator (2) to output on the next high voltage pulse at point 16. If the new value of the load (6) sensed at point (25) remains stable for longer than a predetermined time, for example 1 minute, then it becomes the new value for the steady state load (6). After a predetermined time the energy into the steady state load may be increased.

Figure 7a shows a graphical representation of the low voltage signal generated by the low voltage generator (7), at the output (4, 5) of the energizer (1) of Figures 1 - 5. Figure 7b shows a graphical indication of the impedance of the load (6) on the same time scale.

Figure 7 depicts a situation where the energizer (1) operates in accordance with the description of Figure 6, but where the value of the load (6) drops at point (25), for example from 500 ohms to 100 ohms. The controller (8) is configured to reduce the energy available to the high voltage pulse generator (2) in the manner previously described. Figures 8 and 9 show situations as described with reference to figures 6 and 7 respectively, however in these embodiments the low voltage signal is continually transmitted to the output (4, 5) of the energizer (1).

By transmitting the low voltage signal continually, a change in value in the load (6) may be instantly detected. This is particularly valuable where the detected load (6) indicates a fault condition that requires activation of the alarm device (11).

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT WE CLAIM IS:

1. A method of operating an electric fence energizer, including the steps of:

transmitting a low voltage signal from an output of the energizer onto an electric fence;

determining the load on the electric fence by monitoring the low voltage signal;

determining an appropriate energy level for a high voltage pulse relative to the load; and

generating and transmitting the high voltage pulse from the output of the energizer onto the electric fence according to the energy level determined to be appropriate.

2. The method as claimed in claim 1 , including the steps of:

transmitting a second low voltage signal from the output;

determining the new load on the electric fence by monitoring the second low voltage signal; and

determining an appropriate energy level for the high voltage pulse relative to a change in load.

3. The method as claimed in claim 1 or claim 2, wherein the step of determining the appropriate energy level for the high energy pulse includes comparing the load to a predetermined load value and limiting the appropriate energy level to be lower than a predetermined level if the load is greater than the predetermined load value.

4. The method as claimed in claim 2, wherein the step of determining the appropriate energy level for the high energy pulse includes comparing the change in load to a predetermined change in load value and setting the appropriate energy level to be lower than a predetermined level if the change in load is greater than the predetermined change in load value over a predetermined time.

5. The method as claimed in either claim 2, wherein the step of determining the appropriate energy level for the high energy pulse includes comparing the change in load to a predetermined change in load value and setting the appropriate energy level to be greater than a predetermined level if the change in load is below the predetermined change in load value over a predetermined time.

6. The method as claimed in any one of claims 1 to 5, including the step of verifying the load determined by monitoring the low voltage signal by monitoring the high voltage pulse at the output of the energizer.

7. The method as claimed in claim 6, including the step of setting the appropriate energy level for the high voltage pulse to be lower than a predetermined level and issuing an alarm, if the load determined by monitoring the low voltage signal is not verified.

8. The method as claimed in any one of claims 3 to 5 or claim 7, wherein the predetermined level is 5 Joules.

9. The method as claimed in any one of claims 1 to 8 wherein the low voltage signal is continuously transmitted at all times other than when transmitting the high voltage pulse.

10. The method as claimed in any one of claims 1 to 8 wherein the low voltage signal is transmitted over a predetermined time period prior to transmitting the high voltage pulse.

11. The method as claimed in any one of claims 1 to 10, wherein the low voltage signal is safety extra low voltage, or extra low voltage.

12. The method as claimed in any one of claims 1 to 11 , wherein the low voltage signal contains less than 5% of the energy level determined to be appropriate for the high voltage pulse.

13. An electric fence energizer including:

a controller configured to determine the load on the output of the energizer from the electrical parameter;

a high voltage pulse generator configured to generate and transmit a high voltage pulse from the output of the energizer,

characterised in that the controller is configured to determine an appropriate energy level for the high voltage pulse relative to the load, and control the generation and transmission of the high voltage pulse according to the energy level determined to be appropriate.

14. The electric fence energizer as claimed in claim 13 wherein the low voltage generator is a communications circuit configured to transmit a low voltage communication signal onto an electric fence circuit connected to the output of the energizer.

15. The electric fence energizer as claimed in claim 13 wherein the low voltage generator includes a processor configured to control the high voltage pulse generator to generate the low voltage signal.

16. The electric fence energizer as claimed in any one of claims 13 to 15, including a high voltage sensing device configured to obtain an electrical parameter of the high voltage pulse at the output of the energizer.

17. The electric fence energizer as claimed in any one of claims 13 to 16, including an output transformer having a primary side and a secondary side.

18. The electric fence energizer as claimed in claim 17, wherein the low voltage generator and the low voltage signal device are connected to the primary side of the output transformer.

19. The electric fence energizer as claimed in claim 17, wherein the low voltage generator is connected to the primary side of the output transformer, and the low voltage signal device is connected to the secondary side of the output transformer.

20. The electric fence energizer as claimed in claim 17, wherein the low voltage generator is connected to the secondary side of the output transformer, and the low voltage signal device is connected to the primary side of the output transformer.

21. A computer program configured to be operable by a processor to carry out a method for operating an electric fence energizer, including the steps of:

22. A method of operating an electric fence energizer substantially as herein described with reference to and as illustrated by the accompanying 'Disclosure of Invention' and 'Best Modes for Carrying/Dut the Invention', and drawings.

23. An electric fence energizer substantially as herein described with reference to and as illustrated by the accompanying 'Disclosure of Invention¹ and 'Best Modes for Carrying Out the Invention', and drawings.